PURPOSE: To obtain coincidence between a transmission and a reception frequency automatically when setting received beats to desired pitch by varying the BFO of a receiver, by varying a sine tone oscillation frequency by an equal extent associatively.

CONSTITUTION: An IF signal sent out of an intermediate frequency amplifier and a beat signal from a BFO2 are supplied to a beat detector 1. A detection signal from the beat detector 1 is mixed by a mixer 4 with a side tone from a transmitting side tone 5 and then amplified by a low frequency amplifier 7, allowing a speaker 8 to sound. In this case, the variable capacitor 3 of the BFO2 and the variable capacitor 6 of the transmitting side tone 5 are put in associative operation to allow the frequency of the beat signal from the BFO2 and that of the transmitted side tone to coincide with each other at any time.